Low German regularly changes its final obstruent f to v (IPA: [v]) when a vowel follows: en doof Mann → enen doven Mann. This sound-change is usually kept in standard German pronunciation, although the forms are always spelt with f. (For more words in which written f may be pronounced [v] compare Elfer, Fünfer, and schief.)

The comparation forms with umlaut (döfer, am döfsten) are restricted to colloquial usage.